Magnetic sound translating head



'Dec 14, 1948 I L. B. CORNWELL MAGNETIC SOUND TRANSLATING' HEAD Filed April 5, 1946 L m RL mEMM MW m m A O c A B L W @W L nw vv 9 Patented Dec. 14, 1948 MAGNETIC SOUND TRANSLATING HEAD Lionel B. Cornwell, New Canaan, Gonn.

Application April 3, 1946, Serial No. 659,246

'7 Claims.

This invention relates to electrical sound translating devices of the so-called magnetic type. The invention is useful in translating mechanical motion into electrical impulses, as well as in translating electrical impulses into mechanical motion.

The invention is adapted for use as a microphone or to pick up any motion of a vibratory nature. As exemplified in the present embodiment the invention takes the form of a phono-.

graph pickup and the following disclosure of such embodiment will be sufficient to permit those skilled in the art to understand the invention and the various uses to which it maybe put.

An object of the invention is to provide a relatively simple device of the magnetic type adapted for use with either lateral or vertical cut records, or the like use, and which may be manufactured at a relatively low cost.

Another object of the invention is to provide a device of the type described which will faithfully translate the desired sound free from extraneous disturbances.

Another object of the invention is to provide a simple and eflicient device which will reduce substantially the wear of a record sound track.

The invention consists of the novel features, arrangements, construction and combination of parts embodied, by way of example, in the apparatus to be hereinafter more fully described as illustrating a present preferred form of the invention, and the invention will be more particularly pointed out in the appended claims.

Further and more specific objects, features and advantages of the invention Will more clearly appear from the detailed description to be given following, taken in connection with the accompanying drawings in which:

Fig. 1 is a front elevational View, on an enlarged scale, of a pickup device in which the coil windings are shown somewhat diagrammatically;

Fig. 2 is a side elevational view of the device shown in Fig. 1;

Fig. 3 is a front elevational view illustrating certain modifications of the device shown in Figs. 1 and 2;

Fig. 4 is a sectional view taken at line i4 of Fig. 2; and V Fig. 5 is a somewhat diagrammatic front elevational View to more clearly illustrate certain features of the structure shown in Fig. l and is on a further enlarged scale.

Before describing the invention in detail certain salient features will be referred to by way of introduction. An important feature of the invention resides in the use of a resiliently supported magnetic armature that cannot freeze to any of the magnetized poles and which has unrestricted motion throughout the maximum limits of all lateral and vertical cut phonograph records, e. g. throughout the maximum amplitude of audio frequency. This unlimited travel makes it possible to build into the resilient supporting means for the armature any value of compliance desired without danger of the permanent magnet pulling the armature into an inoperative position. Other important features of the invention are the maintenance of a relatively high density of flux flow through an armature of relatively low mass; the maintenance of a unidirectional flow of flux through the armature; and the bucking out of undesirable coil currents resulting from extraneous electrical disturbances or due to lateral motion of the stylus when reproducing vertical cut records and vice versa.

Referring to the drawings and more particularly to Figs. 1 and 2, the main supporting frame for the device is designated in general as if! and is made of a suitable non-magnetic material such as aluminum, plastic or the like and is provided with an upper arm l l and-a lower arm E2. The upper arm H is provided with a recess in which is seated a permanent magnet :3 providing opposite magnetic poles N and S. A pair of laminated pole pieces Ill and I5 are supported on the arms H-l2 with the upper ends disposed in respective magnetic engagement with the magnet poles N and S and the bottom ends of the pole pieces are disposed in slots such as i 6; the upper ends of the pole pieces being rigidly secured in position by screws I'll8 and the lower ends by screws I949. A pair of auxiliary pole pieces 20-2l have their upper ends clamped against the respective pole pieces Ml 5 and against the arm I I by means of the screws ll--l8. The pole pieces M-l 5 are provided respectively with electrical coils 22-23; the coil 22 being somewhat diagrammatically shown and having terminals 2d25 while the coil 23 is similarly shown and has terminals 262l. The coils are preferably identical in dimension, number of turns and impedance.

The pole pieces M-i5 terminate in lower ends designated Nl-SI which are disposed on a substantially horizontal plane and are spaced apart laterally. The auxiliary pole pieces 20-2! extend downwardly, exterior of the coils 22-43, and then inwardly and terminate in pole ends N2 and S2 which arev disposed beneath the respective pole ends N |SI from which they are spaced a fixed distance by means of spacer blocks 28-29. An armature A is supported between the outer ends of a pair of spring strips 30-3! (Fig. 4) whose rear ends are spaced apart by a spacer block 32 and clamped between a downward projection 33, formed integrally with the arm i2, and a clamping bracket 34 by means of screws, such as 35. The armature and adjacent ends of the spring strips 39-3! are provided with an aligned hole through which a reduced upwardly extending stem of the stylus 36 passes, the head of the stem being riveted over to rigidly hold the stylus in fixed relationship with the armature A. A compliant block 37, made of soft felt or rubber,

is disposed between the head of stylus 35 and the.

clamp plate 38, to which it is preferably cemented, and which is engaged by the lower end of an adjusting screw 39 in threaded engagement with a rigid part of the arm l2.

The frame block It] carries secured thereto a base plate at which is preferably provided with a housing portion 4| to enclose the armature and pole ends and having an opening 32 therein through which the stylus 35 extends and whose movement is accommodated by the openin :22. The plate 68 extends outwardly a suificient distance toserve as an attachment means for the outer end of a hollow supporting arm in which the device is adapted to be carried. Frame l6 also preferably carries electrical connector plugs 43 l which are connected to leads 45-45. The lead i6 is connected to the coil terminal 2 and the lead 45 is connected to a suitable switch (not shown) selectively connecting it to the coil terminal 26 or the coil termina127, as will be more fully pointed out following.

Referring more particularly to Fig. 5, it will be seen'that the pole ends NlSl and N2'S2 are spaced apart an-identical lateral distance defined by the planes D-D and E+-E; and the poles Nl-N2 and Sl-SZ are spaced apart vertically an identical distance defined by the planes 28-3 and CC. The lateral spacing between the opposite sides of the armature A and the respective planes DD and E-E is preferably of the order of .005" to .001; and the vertical spacing between the top and bottom of the armature A and the respective planes B--B' and -6 is preferably of the order of .001" to .008" when the stylus S is in operative neutral position. When the unbalanced weight of the device is thus exerted upon the stylus S which is in engagement with the sound disk, or record, and the armature A is disposed in neutral position between the planes B'B and C-C the armature A is inmagnetic equilibrium. The armature A may be of very small mass; for example, it may havev a thickness of .014", a width laterally of .065" and a length from front to back of .094.

There is shown in Fig. 3 a modification of the pole and arrangement In this embodiment the pole ends SI and S2 are identical with those above described, but instead of using pole ends Nl-NZ, as above described, this embodiment employs a single north pole N which is common to both of the pole ends SI and S2 and which has a pole face of sufiicient vertical extent so that the armature A is always in overlapping relationship with N during its maximum operable movement. It is also noted that in this embodiment the coil 22' is omitted and electrical fluctuations are produced entirely by the coil 23.

Referring to Fig. 5, it is. noted that the spring mounting of armature A is. such that the armaposition the armature A never overlaps the pole ends Sl-S2 but always overlaps the common pole end N.

When it is desired to use the invention for ver-- tical cut records the coil terminals 25 and 23 are connected together and the terminal 45 (Fig. 2) connected to the coil terminal El; the coil terminals 24 and 2? thus being connected to the connector plugs 4 and 43 which are adapted to be connected to a suitable receiving circuit, such as is well known to those skilled in the art. With the device placed in operative position with the stylus 35 on the sound record the armature will be disposed as shown in Fig. 5. Assuming a vertical vibratory force to be applied to the stylus as it moves over the vertical out sound track, the fol-lowing magnetic and consequent electrical action takes place. The armature A moves upward away from thepoles N2-S2 and toward the poles Nl-S l thus reducing the magnetic flux between the poles Nil-S2 and increasing the fiux between the poles Nl-Sl to the same extent. This induces an electrical potential in the coils 22 and 23. When the armature A moves downwardly the flow of fiuX between Ni and Si 'is correspondingiy reduced and the flux flow between the poles N2 and S2 is correspondingly increased, inducing a potential of opposite polarity in the coils and thus completing the full alternation. The coils being connected in series boosting (for vertical motion of the stylus) provide double the voltage of either single coil. However, with the coils thus connected potentials due to torsional movement of the armature will be bucked out, as will be extraneous disturbances. As will be well understood by those skilled in the art, the coils may be connected in parallel boosting, which willalso result in the current alternations of the coils being in phase for verticalmovement of the stylus and out of phase for lateral movement of the stylus.

When the device is to. be used. with lateral out records the terminal-s 2'5 and 21 are connected togather and the terminal. 2-6 will be connected to the plug terminal 45.. so that the potentials due to lateral movement ofthe stylus are additive or boosting, while the potentialsresulting from ancillary vertical movement of the stylus are in bucking relationship and neutralize each other. Similarly, the coils may be connected in parallel boosting for lateral motion of the stylus, as will be well understood by those skilled in the art.

It will be noted that-the flux flow through the armature is uni-directional during the full-operative range of the devicawhether used'for vertical cut or lateral cut records. In the embodiment described with reference to Fig. 3, since only one coil is employed, this embodiment does not possess the feature ofneutralizin the ancillary movements of the stylus, but this embodiment provides a more simplified structure which is capable of operating with either a vertical or lateral cut records to produce useful results.

Because of the absence of flux reversals or variations, eddy currents and hysteresis do not exist ifications, it will be obvious to those skilled in -the art, after understanding my invention, that other changes and modifications may be made therein without departing from the spirit and scope of the invention, and I aim in the appended claims to cover such changes and modifications as are within the scope of the invention.

What I claim is:

1. In a pickup device of the magnetic type, the combination of magnet means having a first pair of pole pieces of opposite polarity providing pole ends spaced apart laterally and a second pair of pole pieces of opposite polarity providing pole ends spaced apart laterally and spaced vertically from said first pair of pole ends, a laterally extending armature disposed entirely Within a field of movement defined by planes representing said lateral and vertical spacing of said pole ends, resilient supporting means for said armature affording vibratile motion of said armature I throughout its operative range and so constructed and arranged that during the maximum movements of said armature it remains entirely within said field of movement, anda signal generating circuit responsive to movement of said armature. 2. In a pickup device of the magnetic type, a magnetic circuit comprising a magnet and a first and a second pair of pole pieces energized thereby, said first pair of pole pieces providin pole ends of opposite polarity spaced apart laterally and said secured pair of pole pieces providing pole ends of opposite polarity spaced apart laterally and disposed vertically from said first pair of pole ends of respectively corresponding polarity to thereby provide two paths of flux flowing in the same direction, an armature having a lateral extent less than the lateral spacing of said two pairs of pole ends and disposed entirely within said space intermediate said flux paths and supported for vibratile motion relative thereto in relatively opposite directions from a neutral position of magnetic equilibrium, said armature being so disposed and supported relative to said pole ends that during its maximum operative movement it vibrates entirely within the limits defined by four planes bounding the innermost extremities of said four pole ends, and a signal generating circuit responsive to said armature vibrations.

3. In a pickup device of the magnetic type, a plurality of pole pieces comprising laterally spaced poles of opposite polarity and vertically spaced poles of like polarity jointly providing a pair of laterally disposed air gaps spaced vertically one from the other, means for supplying magnetic flux across said air gaps in the same direction of flow, an armature having rigidly secured thereto a stylus for engaging a sound record, said armature being disposed entirely within the space defined jointly by said laterally and vertically spaced poles, means for resiliently supporting said armature in the field of influence of said flux for rocking motion about an axis extending substantially 6 normal to the direction of fiux flow across said gaps and in a plane substantially parallel to the direction of said flux flow, said supporting means also providing for movement of said armature in a direction normal tosaid plane while preventing bodily movement in a direction parallel to said flux flow, said armature and its resilient supporti 10 Having thus described my invention with paring means being so constructed and arranged that when said device is resting on its stylus in operative neutral position said armature is in substantial parallelism and magnetic equilibrium relative to said flux fiow and during its maximum operative movements modulates said fiux flow solely by variation in the space between said armature and respective of said pole pieces of opposite polarity, and a signal generating circuit responsive to operative movements of said armature.

4. A sound translating device of the magnetic typecomprising, a magnetic circuit providing a magnetic flux path and having a pair of laterally spaced pole ends whose lower'faces are disposed substantially on the same plane, said magnetic circuit also providing an auxiliary flux path including a pair of laterally spaced auxiliary pole ends across which flux flows in the same lateral direction as the fluxflow across said first pairof pole ends and whose upper facesare disposed substantially on a plane spaced vertically from said firstplane, an armature positioned for vibratile motion relative to said pole ends, said armature being disposed entirely within the space defined by said lateral spacing of'said pole ends, a stylus rigidly-secured to said armature and providing means for operative engagement with a sound record to thereby transmit "motion between said armature and record, and resilient means supporting said armature and urgingsaid armature away from said upper pole ends with a predetermined force such that with said stylus in neutral operative engagement with a record said armature will be disposed intermediate said planes and will lie substantially parallel to said planes on which said pole faces are disposed and will be spaced downwardly from said upper plane and upwardly from said lower plane.

5. A sound translating device of the magnetic type comprising, a magnetic circuit providing a magnetic flux path and having a pair of laterally spaced pole ends whose lower faces are disposed substantially on the same plane, said mag-' netic circuit also providing an auxiliary flux path includin a pair of laterally spaced auxiliary pole ends across which flux fiows in the same lateral direction as the flux flow across said first pair of pole ends and whose upper faces are disposed substantially on a plane spaced vertically from said first plane, an armature positioned for vibratile motion relative to said pole ends, said armature being disposed entirely within the space defined by said lateral spacing of said pole ends, a stylus rigidly secured to said armature and providing means for operative engagement with a sound record to thereby transmit motion between said armature and record, and resilient means supporting said armature and urging said armature away from said upper pole ends with a predetermined force such that with said stylus in neutral operative engagement with a record said armature will be disposed intermediate said planes and will lie substantially parallel to said planes on which said pole faces are disposed and will be spaced downwardly from said upper plane and upwardly from said lower plane respective distances at least as great as the maximum distance anoasss of operative: movement of said armature toward :saidirespective-pairstotupperand lower pole ends.

6-. A sound; translating device of: the magnetic type comprising; a magnetic circuit providing a magnetic fiuxpathand havin a pair of laterally spaced pole. ends whose lower facesare disposed 'substantiallyon. the same: plane, said magnetic circuit also providing an auxiliary flux path including a pairof; laterally spaced auxiliary pole ends across which flux. flowsiin the same lateral:

direction as thezflux flow across said first pair of pole ends and whose upper faces are disposed substantially on. a; plane spaced vertically from said? first plane, saidtwopairs ofv pole ends being spaced laterally substantially the same distance, an armature positioned for vibrati-le motion relative tosaid pole ends, said armature having a lateral extent less than the lateral spacing of said two pairsiofpoie ends, a stylus rigidly secured tosaid armature and providing means for operative engagement withia. sound record to thereby transmit motion between said armature and record, and resilient means supporting said armature and urging said armature away from said upper pole? ends: with apredetermined force; such.

pole faces are disposed and will be spaced down-- wardly from said upper plane and upwardly from saidlowerplane 7.. A sound transating device of themagnetic type comprising, a. magnetic circuit providing, a

magnetic duxpathaandi having a pair of laterally spaced. pole ends whose lower faces are disposed substantially on thesame plane; said magnetic circuit also providing. an auxiliary flux path including a pair of laterally spaced auxiliary pole ends across: which flux flows in" the same lateral:

direction as the flux flow across said firstpair of pole: end and whoseupper faces are disposedisubstantially on a plane spaced vertically from said first plane, an armature positioned for vibratile motionrelative to. said pole ends, said armature having a lateral extent less than the lateral spacing of said twopairs of pole ends, a stylus rigidly secured to saidL armature and providing means for operative engagementwith a sound record to thereby transmit motion between said armature and record, and resilient means supporting said armature and urging said armature away from said upper pole ends with a predeterminedforce such that with said stylus in neutral operative engagement with a record said armature will be disposed intermediate said planes and will lie substantially parallel to said planes on which said pole faces are disposed: and will be spaced downwardy from said upper plane and." upwardly from said lower plane, said resilient-supporting means affording torsional movement of said armature about an axis substantially parallel-to said planes and extending in a direction normal to said flux flow across said pole ends responsive to lateral movement of said stylus.

LIONELB. CORNWELL.

REFERENCES CITED The following, references file of this patent:

UNITED STATES PATENTS are of record in the 

